Thermoswitch



N. J. SMITH THERMOSWITCH Apri'a 17, 1945.

Filed Dec. 31, 1943 2 Sheets-Sheet m\ w Q N u mw E ,S Ll mw mw www NM mw 555555,55, w RMN N S uw \\m\\\\\\ kw TW ha mw N. J. SMITH THERMOSWITCH pr i7, 1945o 2 Sheets-Sheet 2 Filed Deo. 31, 1943 Patented Apr. 17, 1945 THERMOSWITCH Norman J. Smith, Medeld, Mass., assignor to Fenwal Incorporated, Ashland, Mass., a corporation of Massachusetts Application December 31, 1943, Serial No. 516,603

(Cl. 20D-137) 10 Claims.

This invention relates to circuit controlling thermoswitches whereby apparatus in circuit with the switch maybe controlled to regulate the temperature of a device, such as the engine of an airplane.

The principal object of the invention is to provide a midget thermoswitch which may be preset at the factory to respond to a given temperature n and cannot thereafter be adjusted by the user, or

which may be adjusted at will by the user.

My invention comprises a stretchable element and a strut, the ends of which are secured to said element, said strut and elementv having different coefficients of expansion, and a sliding element arranged for co-operation with a contact on the strut for adjusting the switch to respond to any desired temperature.

In the accompanying drawings,

Figure lis a central longitudinal section of a thermoswitch embodying that form of my inven, tion wherein the switch may be adjusted by the user, the scale being four times actual size.

Fig. 2 is an end View.

Fig. 3 is a transverse section taken on the line 3 3 of Fig. ll, the scale being eight times actual size.

Fig. a is a central longitudinal section of an embodiment of my invention wherein the switch is preset at the factoryfand cannot thereafter be adjusted by the user.

In the particular drawings selected for more fully disclosing the principle underlying the invention and which are to be considered as illustrative, merely, and not restrictive, I is a stretchable member consisting in the present instance of a block of suitable metal having a relatively high coeiicientA of expansion, such as brass, which has been milled out to provide a rectangular trough II withinwhich is disposed astrut I2 of invar, or other suitable material, having a very small or practically zero coeicient of expansion.

In the present instance, the outer wall of the member I0 is arcuate to facilitate'its insertion in the cylindrical casing I3 between which and said member is interposed a sheet of insulation I4.

In any suitable manner, such as by soldering or electric welding, the ends of the strut are rigidly secured to the respective ends of the stretchable member I0.

Disposed above the strut is a longitudinally movable cam contact member I5, shown in the present instance as attached to the underside of a slidable bar I6 by the pin I1, said bar resting.

on the strips of mica or other suitable insulation material I8 which lie on the flattened end portions I0' of the member I0.

The slidable contact memberr is disposed for cooperation with the contact member I9 secured to the mid portion of the strut, and, in the present instancey the under surface thereof is inclined to the axis of the switch. Whilevany suitable means may be employf i for moving the bar longitudinally and thereby changing the relative positions of the two contact members, I have shown in the present instance a screw 20 having threaded engagement with a flange 2l integral with the bar anddisposed at right angles thereto. The screw is rotatable within the insulation collar 22 around one end of which is spun the end of the hollow plug 23 as indicated at 24, and the right-hand end of the casing I3 is pressed into a peripheral groove in said plug, as shown at 25. The end of the flange is guided by the flat 2l formed on the lower wall of the plug 23 and is insulated therefrom by the strip 23. A cap 26 is threaded to the plug 23 to afford ready access to the screw 20 and protect the same after adjustment thereof.

Suitable insulation 2l is provided for preventing electrical contact between the casing and the arcuate sliding bar, and insulating discs 28 are placed between the ends of the thermoswitch element I0 and the parts adjacent thereto. The left-hand end of the thermoswitch is closed by the insulation plug 29 through which pass the lead wire tabs 30, 3 I, the former being electrically and mechanically connected in any suitable manner to the switch element IIJ, and a portion of the latter being bowed upwardly into engagement with the sliding bar I6.

An indicating or an actuating device 32 and battery 33 are shown in circuit with the lead wiretabs as indicative of a circuit controlled by the thermoswitch.

When the midget switch is used to control the temperature of the engines of a dive bomber, the element 32 will be a suitable device for actuating the louvres or other ventilators in the cock pit of an airplane.

It will be obvious that when the position of the slide 20 is adjusted to place the contact members I2 and I5 in the position shown, the circuit will inverse thermoswitch, whereby the circuit is closed when the temperature rises to a predetermined value. In this case, the strut 40 is bowed downwardly and Provided with a contact member Y ti disposed for co-operation with the movable i3 and the ends thereof are insulated from the adjacent parts by the mica washers 28, as in the case of the direct thermoswitch described in con-v nection with Fig. 1. There is, however, no insulation between the bai' i t and the casing. The lefthand end of the member i3 terminates in a contact making prong di which is enclosed within the metallic cylinder 65, the prong and cylinder forming aA socket whereby the two thermoswitch elements are connected to the circuit which is` to be controlled. The socket aforesaid may be threaded to the thermoswitch casing and held in position by the drive pins t5. An interiorly threaded coupler having a iiange di engaging the shoulder de formed in said socket may be employed to secure said socket to the co-operating elements in which the ends of the controlled circuit terminate, said` circuit being represented conventionally in the same manner as in 1; but, in the present instance, both terminals of said circuit are grounded, for example, on the body of the airplane engine or other apparatus the temperature of which is to be controlled.

, InFig. 4 the protecting cap @Sis permanently secured to the thermoswitch casing by rolling a peripheral portion 5t thereof into a co-operating groove in the end plug 5i. The ends of the strut di) are secured in any suitable manner to the respective ends of the thermoswitch member E3. It will be noted that said strut is in electrical contact with the prong dit and that the slide bar it is in electrical contact with the socket l5 by way of the extension thereof which is threaded to the casing. v In Fig. 1, the expansible trough-shaped thermostatic member i0 having thickened end portions I0' and the Strut IZconstitute a unitary `preconstructed thermostatic element in which the ends of the strut supported by said end portions lie, after the insertion of said element in the casing I3, on the opposite side of the longitudinal axis of the casing from the cam contact member.

In Fig'. 4, the expansible trough-shaped thermostatic member'43 and strut 40 constitute a unitary preconstructed 'thermostatic element in which Ythe ends of the strut supported by the atraso? ing dierent coecients of expansion, the ends of said strut being secured to the respective ends of said stretchable element, the combinationof an enclosing casing, a contact member on said strut said strut being independent oi.' said casing, a longitudinally movable cam contact member disposed for co-operation with the contact member on said strut means electrically connecting said strut and said stretchable element to one pole of an electric source, means electrically connecting said cam contact member to the other pole of said source, and means for varying the position of said cam contact member with respect to the contact memsaid cam contact member to the other pole of said source, and means for varying the relative position of said contact members.

3. A thermoswitch, comprising in combination, an enclosing casing, a thermally responsive ele-` ment, a strut independent of said casing and provided with a contact member, said strut having a coefficient of expansion diderent from that of said thermally responsive element, a longitudinally movable cam contact member disposed for co-operation with the contact member iirst mentioned, means electrically connecting said strut and said thermally responsive element to one pole of an electric source, means electrically connecting said cam contact member to the other pole of said source, and means for changing the position of said cam contact member with respect to the contact memberco-o'perating therewith.

4. A thermoswitch, comprising in combination, an enclosing casing, two elements having diierent coemcients of expansion, means securing the ends of one of said elements to the respective ends of the other, a contact member on one of said elements, a slide disposed for longitudinal movement with respect to said contact member, a contact member secured to said slide and having a surface inclined to the axis thereof, said contact members being disposed for co-operation,

' each of said elements being independent of said thickened end portions of said member lie, after f the insertion of said element in the casing i3', on the sameV side of the longitudinal axis of the casing as said cam contact member.

- In both cases, saidpreconstructed thermostatic element in combination with the enclosing casing `from which it is insulated and with which is associated a contact member co-operating with that of the thermostatic element, constitute a thermoswitch of very small dimensions wherein the casing has no eiect on the movement of the strut. By virtue of this arrangement, the assembly of the midget switch is greatly facilitated.

Having thus described illustrative embodiments of my invention without, however, limiting the same thereto, what I claim and desire to secure by Letters Patent is: f

l. In a thermoswitch, comprising a stretchable element and a strut, said element and strut hav-f casing, and means for moving said slide longitudinally.

5. A thermoswitch, comprising a unitary preconstructed thermostatic element consisting of an expansible trough-shaped thermostatic member having thickened end portions, a strut, the

respective ends of said strut being supported on` 6. A thermoswitch comprising in combination,

a unitary preconstructed thermostatic unit having a strut provided with a contact member intermediate the ends thereof, means securing the ends of said strut to the respective ends oi said 7d unit, insulation members disposed on the ends of said unit, a longitudinally extending slide disposed on said insulation members, a cam contact member secured to said slide and disposed for,

co-operation with the contact member on said strut, an enclosing casing, screw means in threaded engagement with said slide for adjusting the longitudinal position thereof, a collar laffording a bearing for said screw, and means securing said collar to said casing.

'7. A thermoswitch comprising in combination, a unitary preconstructed thermostatic unit having a strut provided with a contact member intermediate the ends thereof, means securing the ends of said strut to the respective ends of said unit, insulation members disposed on the ends of said unit, a longitudinally extending slide disposed on said insulation members, a cam contact member secured to said slide'and disposed for co-operation with the contact member on said strut, an enclosing casing, and means for moving said slide longitudinally of said strut, a collar supporting the means last named, and means securing said collar to said casing.

8. A thermoswitch comprising in combination, a unitary preconstructed thermostatic unit having a strut provided with a contact member intermediate the'ends thereof, means securing `the ends of said strut to the respective ends of said unit, insulation members disposed on the ends of said unit, a longitudinally extending slide disposed on said insulation members, a cam contact member secured to said slide and disposed for co-operation with the contact member on said strut, an enclosing casing, a flange on the end of said slide disposed transversely of the axis of said casing, a screw in threaded engagement with said flange for adjusting the longitudinal position thereof, a collar aording a bearing for said screw, means securing said collar to said casing, and means for supporting and guiding the end of said flange.

9. A direct thermoswitch, comprising a unitary preconstructed thermostatic element consisting of an expansible trough-shaped thermostatic member having thickened end portions, and a strut, the respective ends of said strut being supported on said end portions, and a contact member on said strut, in combination with an enclosing casing, and a cam contact member co-operating with the contact member of said strut, the ends of said strut lying on the opposite side oi' the axis of said casing from said cam contact member, said strut and trough-shaped member having different coeiiicients of expansion.

10. An inverse thermoswitch, comprising a unitary preconstructed thermostatic element consisting of an expansible trough-shaped thermostatic member having thickened end portions, and a strut, the respective ends of said strut being supported on said end portions, and a contact member on said strut, in combination with an enclosing casing, and a cam contact member c0- operating with the contact member of said strut, the ends of said strut lying on the same side of the axis of said casing as said cam contact member, said strut and trough-shaped member having different coelcients of expansion.

NORMAN J. SMITH. 

